Your very right. A historian that I heard recently states that the phrase separation of church and state is not found in any of the original American historical documents, including personal correspondence. It is found in the communist manifesto.
Thomas Jefferson. That "historian" is full of it.
It was landmark U.S. Supreme Court precedent Reynolds v. United States in 1878 that made "separation of church and state" a dubiously legitimate point of case law, but more importantly, it confirmed the Constitutionality in statutory regulation of marriage practices (as far as the court is concerned).